Stents with attached looped ends

ABSTRACT

An open frame prosthesis is formed with looped end terminations at its proximal and distal ends. At one end of the prosthesis, the filaments or strands are welded together in pairs to form strand couplings. A plurality of loop segments are connected to the strand couplings, one loop segment for each pair of adjacent strand couplings. In one version of the prosthesis, strands at the opposite end are bent to form looped ends. In another version, loop segments are connected to pairs of strand couplings at both ends of the prosthesis. The loop segments can be connected to the couplings by welding, fusion bonds, or tubes, which are either crimped or heat shrunk.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 13/339,756, filed Dec. 29, 2011, which is adivisional application of U.S. patent application Ser. No. 12/649,843,filed Dec. 30, 2009, now U.S. Pat. No. 8,109,988, which is acontinuation of U.S. patent application Ser. No. 10/852,495, filed May24, 2004, now U.S. Pat. No. 7,655,039, which claims the benefit of U.S.provisional application Ser. No. 60/472,929, entitled “Stents WithWelded Looped Ends,” filed May 23, 2003, which are each incorporatedherein by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to stents and other body insertabledevices of open frame construction, and more particularly to radiallyexpandable or radially self-expanding prostheses.

BACKGROUND OF THE INVENTION

A variety of treatment and diagnostic procedures involve the use ofdevices intraluminally implantable into the body of the patient. Amongthese devices are stents, such as disclosed in U.S. Pat. No. 4,655,771(Wallsten). This type of prosthesis, shown in FIG. 1, is a tubular,braided structure formed of thread elements wound helically in oppositedirections. The stent is shown in a relaxed state, i.e. in theconfiguration assumed when the stent is subject to no external stress.The stent is elastically compressible to a reduced-radius, axiallyelongated state to facilitate an intraluminal delivery of the stent toan intended treatment site. At the site, the stent is released forradial self-expansion into contact with surrounding tissue, for examplea blood vessel wall. The stent does not fully expand, but insteadremains under a slight elastic compression, so that an internal elasticrestoring force tends to anchor the stent within the vessel, andmaintain vessel patency.

The thread elements, also called strands or filaments, form multipleintersections or crossing points, each including a pair of oppositelydirected strands. At each end of the stent, oppositely directed strandsare connected in pairs to form end terminations or strand couplings. Thestrands can be formed of metal, in which case the end terminations canbe formed by welding the strands or by twisting the pairs of strandstogether, preferably augmented with welds. Alternatively, the strandscan be formed of polymeric materials, with end terminations formed byfusing the strands or boding them with an adhesive.

As an alternative to self-expanding stents, a malleable metal such astantalum can be wound or braided into a plastically deformableprosthesis. This device is capable of maintaining a reduced-radius stateon its own to facilitate delivery, but requires a balloon or otherimplement to expand the prosthesis into contact with surrounding tissueat the treatment site.

FIG. 2 illustrates part of a prosthesis formed according to analternative construction in which the strands are wound instead ofbraided, to form generally hexagonal cells. Adjacent cells havecoextensive regions, along which pairs of the strands are wrappedhelically about one another. This construction is further illustratedand explained in U.S. Pat. No. 5,800,519 (Sandock).

FIG. 3 illustrates a prosthesis formed according to anotherconstruction, illustrated and discussed in U.S. Pat. No. 6,264,689(Colgan). Like the stent in FIG. 2, this stent features structuralstrands wound to form multiple helical cells. However, it differs fromthe device of FIG. 2, in that at some of the junctions of strands, thestrands simply cross one another, rather than being twisted helicallyabout one another.

At a distal end of the prosthesis in FIG. 3, the strands are bent toform a plurality of loops 1. These loops form relatively flexible, bluntend terminations, desirable because they more readily adjust to featuresof the body lumen in which the prosthesis is deployed, and they presentminimal risk of injury to the surrounding tissue. Conversely, at theproximal end, pairs of strands are twisted together and ball welded atthe ends, to form proximal end terminations 2.

The devices in FIGS. 1 and 2 may also be formed with distal and proximalend terminations comprising bends and twisted pairs, respectively.Alternatively, any of these devices may be formed with twisted endterminations at both the proximal and distal ends. As a furtheralternative, terminations at the proximal end, or at both ends, may beformed by welding the pairs of strands together, without twisting.

In any event, while these stents are well suited for a variety ofprocedures, the welded or twisted end terminations are disadvantageous.As compared to the rest of the prosthesis, the welded or twisted endterminations are relatively stiff and rigid, and thus more likely topoke surrounding tissue, rather than bend to accommodate the tissue.Because of the abrupt ends of the welded or twisted end terminations,the poking occasioned by their relative stiffness presents a risk ofdamage to tissue. Consequently, any positional adjustment of a deployedstent, particularly in the direction that the welded or twisted endterminations extend, is difficult. Another problem encountered with thetwisted or welded end terminations is that adjacent twisted wire pairsmay interlock when the stent is radially compressed into the deliverystate, and then interfere with radial expansion of the stent at atreatment site.

When the stent or other prosthesis is constructed by bending the strandsat its distal end, the situation is improved somewhat by limiting theforegoing difficulties to the proximal side. While they are reduced,these difficulties remain, most notably to prevent any substantialproximal repositioning of a deployed stent. Further, even the loopeddistal end of such device presents a problem that can limit its use. Inparticular, radial contraction of the device requires each loop to bend,primarily at its distal apex. The extent of radial reduction is limitedby the extent to which each loop can be bent.

Therefore, it is an object of the present invention to provide aprosthesis of open frame construction with blunt, flexible endterminations at both of its opposite ends, to permit movement of thedeployed prosthesis relative to surrounding tissue in either axialdirection, with minimal risk of trauma to the tissue.

Another object is to provide a prosthesis with looped end terminationsthat permit radial compression of the prosthesis to a smaller diameterfor intraluminal delivery.

A further object is to provide a process for fabricating a stent withthe elongate strands or strand segments selectively shaped at one orboth ends of the stent to provide relatively blunt and flexible endterminations.

Yet another object is to provide a stent or other prosthesis that ismore readily adjustable and retrievable after its deployment in a bloodvessel or other body lumen.

SUMMARY OF THE INVENTION

To achieve the foregoing objects and others, there is provided animplantable prosthesis. The prosthesis includes a plurality of elongatestrands cooperating to form an open-frame tubular structure radiallyexpandable and contractible between an enlarged-radius state and areduced-radius state. Different ones of the elongate strands areintegrally coupled to one another along respective end regions thereofto form a plurality of strand couplings along a selected end of thetubular structure. A closure member is connected to a pair of associatedstrand couplings, and extends between the associated strand couplings toform a loop segment directed axially outwardly from the associatedstrand couplings.

In a preferred arrangement, each of the strand couplings is formed byjoining two of the strands along their respective end regions, thestrands form an even number of strand couplings, and the number ofclosure members is equal to one-half the number of strand couplings.Each closure member is connected to a different pair of the couplings;i.e. one end termination loop for every four strand ends.

For comparison, when the looped end terminations are formed by bendingthe strands as shown at 1 in FIG. 3, twice as many looped endterminations are required. Thus, looped end terminations formedaccording to the invention, although larger than the conventional loopedend terminations, permit a similarly sized stent to be radiallycontracted to a smaller size, due to the lower number of looped endterminations.

In one advantageous form of the prosthesis, each pair of associatedstrand couplings includes a first strand coupling in which the ends ofthe coupled strands substantially coincide, and a second strand couplingin which one of the strands extends beyond the other to provide a strandextension of a predetermined length. The strand extension is selectivelyshaped and connected to the first strand coupling, preferably bywelding, to provide the loop segment.

Other suitable means for connecting the closure members and strandcouplings include fusion bonds, adhesives, and tubes surroundingadjacent portions of the closure member and strand coupling.

Preferably, each closure member is somewhat U-shaped, comprisingopposite legs, each coupled to one of the paired strand couplings, and amedial region between the two legs. The medial region can be shaped toincorporate two inclined side sections and a curved apex between theside sections. As the tubular structure is radially contracted, eachclosure member tends to bend primarily at the apex, and along regions ofslight curvature between the side sections and legs.

While shown and described primarily with braided and wound tubularstructures, end closure members in accordance with the present inventioncan be employed to enhance virtually any open-frame structure havingstrand couplings at one of its ends, to render that end more flexibleand reduce the risk of trauma to surrounding tissue.

Another aspect of the invention is a body implantable device, includinga plurality of elongate strands wound to form an open-frame tubular bodyradially expandable and contractible between enlarged-radius andreduced-radius states. At one end of the tubular body, the strands arecoupled integrally with respect to one another to form a plurality ofstrand end couplings arranged circumferentially about the selected end.A plurality of closure members are individually associated with pairs ofthe strand end couplings. Each closure member is connected to itsassociated pair of the couplings, and extends from a first one of thecouplings to a second one of the couplings to form a loop segmentdirected axially outwardly from the associated pair.

Another aspect of the present invention is a process for forming a bodyimplantable device with at least one atraumatic end, including: windinga plurality of elongate structural strands to form an open-frame tubularstructure having first and second opposite ends; along a first one ofsaid opposite ends, integrally coupling different ones of the elongatestructural strands together along respective end regions thereof to forma plurality of strand couplings, wherein each of the strand couplingsincludes at least two of the strands; and shaping an elongate strandsegment into a loop segment having an arcuate region, and forming aconnection of the strand segment with an associated pair of the strandcouplings, with the arcuate region disposed axially outwardly of theassociated strand couplings.

Thus in accordance with the present invention, a stent or otheropen-frame prosthesis is fashioned with flexible, blunt, atraumaticends, so that after its deployment in a body lumen, the device ismovable without the risk of injury to surrounding tissue. As compared tosimilarly sized devices with conventional looped end construction,devices constructed according to the invention are compressible radiallyinto smaller diameters to facilitate their intraluminal delivery. Thelooped end terminations described herein can be formed at either end orboth ends of stents and other open-frame prostheses.

BRIEF DESCRIPTION OF THE DRAWINGS

For a further understanding of the above and other features andadvantages, reference is made to the following detailed description andto the drawings, in which:

FIG. 1 is a side view of a conventional braided stent;

FIGS. 2 and 3 illustrate known alternative open frame prosthesisconstructions;

FIG. 4 is a side view, partially in section, showing a braided stentconstructed according to the present invention, contained within adeployment and delivery device;

FIG. 5 is a side view of the stent of FIG. 4, in a relaxed state;

FIG. 6 is an enlarged view of one end of the stent;

FIG. 7 is a proximal end view of the stent;

FIGS. 8-10 illustrate several stages in the fabrication of the stent;

FIGS. 11-15 illustrate end regions of alternative embodiment prostheses;

FIG. 16 is a side view of a further alternative embodiment prosthesiswith welded loops at both ends; and

FIG. 17 illustrates a component for positionally adjusting or retrievingthe stent of FIG. 16 after its deployment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now to the drawings, there is shown in FIG. 4 a stent 16fabricated according to the present invention, and part of a device 18used to intraluminally deliver the stent to an intended treatment siteand deploy the stent at the treatment site.

The device includes an elongate, flexible outer catheter 20 having adistal end region 22, along which the outer catheter surrounds stent 16and maintains the stent in a reduced-radius, axially elongated deliverystate to facilitate an intraluminal delivery of the stent to thetreatment site.

Stent 16 is contained within a lumen 24, which runs substantially theentire length of the outer catheter. An inner catheter 26, contained inthe lumen, extends lengthwise along the outer catheter and is moveableaxially relative to the outer catheter. A deployment member 28 is fixedto inner catheter 26, proximally of stent 16. Inner catheter 26 includesa lumen (not shown) to accommodate a guidewire 30, which is used toguide the inner and outer catheters to the treatment site. When outercatheter 20 is moved proximally relative to inner catheter 26, thedeployment member is encountered by the proximal end of the stent,whereupon further proximal movement of the outer catheter progressivelyreleases the stent from the outer catheter, allowing the stent toradially self-expand into contact with surrounding tissue.

Stent 16 is composed of oppositely directed helically wound strands orfilaments 32 that intersect one another to form multiple intersectionsor crossing points. Strands 32 are interbraided in a one-over-one-underpattern. At the distal end of stent 16, strands 32 are bent to formdistal end loops 33. Preferably the strands are formed of a superelasticalloy of titanium and nickel sold under the brand name Nitinol. Othersuitable strand materials include cobalt-based alloys such as those soldunder the brand names Elgiloy or Phynox, MP35N alloy, and certainstainless steels. Suitable nonmetallic alternatives include polymers,for example polyester and polyethylene terephthalate (PET).

Strands 32 are resilient, and when maintained as shown in FIG. 4 storean elastic restoring force. When released from outer catheter 20, stent16 self-expands under the restoring force, toward a normal or relaxedstate shown in FIG. 5 that stent 16 assumes when under no externalstress. As a result of its braided construction and helical strandshapes, stent 16 shortens axially as it expands radially. When thedeployed in a blood vessel or other body lumen, stent 16 engagessurrounding tissue before it expands fully to the relaxed state. Thus,the deployed stent exerts a radially outward force against the tissuethat tends to anchor the stent at the treatment site.

One of the challenges to the physician using device 18 is to accuratelyplace the stent. Accurate placement is made more difficult by the axialshortening of the stent as it enlarges radially. Once the stent is fullydeployed, it is contiguous with and frequently partially embedded intothe surrounding tissue. As a result, it is difficult to adjust theposition of the stent to correct a less than accurate placement. Withprostheses constructed as shown in FIGS. 1-3, proximal stent adjustmentis particularly difficult because of the stiff welded and/or twistedstrand couplings with abrupt proximal ends that present the risk ofinjury to tissue.

In accordance with the present invention, the proximal end of stent 16is formed with a series of loop segments. Specifically, six loopsegments 34-44 are formed in conjunction with twelve strand junctions orcouplings 46. Each loop segment acts as a closure member, cooperatingwith its associated pair of strand couplings and the coupled strands toform a closed loop end termination. Each loop segment is formed with anextension of one of the coupled strands. For example, FIG. 6 shows astrand junction 46 a including strands 32 a and 32 b, coupled to eachother by a weld 48. Similarly, strands 32 c and 32 d are joined by aweld 50 to form a strand junction 46 b.

Strand 32 b is longer than the other strands by a predetermined length,to provide a proximal strand extension or portion 52 extending beyondthe other strands, which is shaped to provide loop segment 34. Loopsegment 34 has several discrete elements, including opposed axiallyextending legs 54 and 56, opposite inclined linear side sections 58 and60, a curved proximal end apex 62, and a pair of arcuate sections 64 and66, each between one of the legs and side sections. A portion of leg 56is axially aligned with junction 46 b, and is connected to that couplingby a weld 68. The remaining loop segments 34-44 are formed in the samemanner.

Stent 16 after deployment can be moved proximally along the body lumenwithout the risk of trauma to the surrounding tissue. Apex 62 and itscounterparts on the other loop segments provide smooth, rounded, bluntproximal end terminations with no tendency to poke or cut into tissue asthe stent is moved. Also, the loop segments are considerably moreflexible than the strand end junctions, regardless of whether thestrands are twisted. This is primarily due to strands 32, which arebendable about tangential axes both proximally and distally of junctions46 to carry apex 62 and its counterparts radially inward. This affords alocalized (proximal) radial contraction of the stent to facilitatepulling the stent proximally along the lumen while the majority of thestent remains in contact with surrounding tissue.

Apex 62 further is bendable about radial axes, to bring the legs andside sections closer to one another during radial contraction. Arcuatesections 64 and 66 also are bendable about radial axes, although unlikethe apex, they bend in the direction of increasing radii of curvatureduring radial contraction of the stent. As a result, legs 54 and 56 tendto retain their axial orientation during radial contraction of thestent.

As illustrated in FIG. 7, loop segments 34-44 are arranged symmetricallyabout the proximal end of the stent, equally angularly spaced apart fromone another. Radial contraction of stent 16 not only bends each loopsegment into a narrower configuration, but also reduces the gaps betweenadjacent loop segments. The extent of permitted radial contraction islimited by the amount of bending permitted in each loop segment,particularly at the apex. A salient feature of the present invention isthe association of single loop segments with pairs of strand junctions,which reduces the number of loops by one-half, as compared to theconventional loops formed by bending the strands at one end of thestent. Thus, the proximal end of stent 16, as compared to its distalend, is contractible to a smaller diameter.

Stent 16 is fabricated, first by helically winding strands 32 onto ashaping mandrel 70. While FIG. 8 shows only one strand 32 a wound aboutthe mandrel, it is to be appreciated that all of the strands are woundsimultaneously onto the mandrel to form the braided structure. From afirst end 72, strand 32 a is wound helically about mandrel 70 until itapproaches a remote end 76 of the mandrel, where the strand is trainedabout a pin 78 to form one of bends 33. Then, the strand is woundhelically about the mandrel in the opposite direction, to a proximateend 82. Each strand forms two helical runs or passes over the axiallength of the stent. In stent 16, twelve strands form twenty-four suchruns. At the proximal end of the mandrel, the ends of the strands formtwelve junctions 46.

FIG. 9 shows two of the strand junctions, representing four strand ends,disposed on mandrel 70. Strand 32 b includes portion 52 extendingaxially beyond the rest of the strands. Three pins 84 are fixed to themandrel, axially outwardly of the strand couplings. Extension 52 ofstrand 32 b is bent about each of pins 84. Its free end 86 is positionedagainst strand 32 c, then attached to strand 32 c by welding.

At this stage, mandrel 70 is placed in an oven (or the mandrel isheated) to a heat the strands to a heat set temperature. The heat settemperature, while much lower than the melting temperature for thestrand material, is sufficient to relax the strands such that they areamenable to shaping. When the braided structure cools after heatsetting, each strand retains its helical shape, and the strandscooperate to determine the relaxed-state tubular shape of the braidedstructure. Shape memory alloys such as Nitinol are particularly wellsuited for this process.

FIG. 11 is a view similar to that in FIG. 6, showing part of a stent 90with an alternative loop forming arrangement in which a strand 92 a(rather than 92 b) is longer than the other strands and provides theloop segment. In addition, a free end 94 of strand 92 a is positionedadjacent strand 92 d, rather than 92 c, then welded to a junction 96 bas before. This can be conveniently considered and “outside-to-outside”connection, as opposed to the “inside-to-inside” connection shown inFIG. 6. For stents of a given size, outside-to-outside connections formslightly wider loop segments.

FIG. 12 shows another alternative arrangement in which hypotubes areused in lieu of welds to secure adjacent portions of the strands. Theconnections for one of the loop segments are formed by sliding ahypotube 98 over strands 100 a and 10 b, sliding a hypotube 102 overstrands 100 c and 100 d, shaping an extension 104 of strand 100 b andinserting its free end into hypotube 102, then crimping the hypotubes toprovide a friction fit that anchors the strands to one another. Thehypotubes preferably are formed of steel.

In similar alternative arrangements, tubes 98 and 102 can be formed ofelastomeric materials and provide a friction fit, augmented with anadhesive if desired. In another alternative, tubes 98 and 102 are heatshrunk onto the adjacent strands.

FIG. 13 shows part of the proximal end of a polymeric stent 106,specifically polymeric strands 108 a and 108 b forming a junction 110 a,and polymeric strands 108 c and 108 d forming a junction 110 b. Thestrand junctions are formed by fusion bonding. In addition, an extension112 of strand 108 b is shaped to provide a loop segment, and its freeend is connected to strand 108 c, again by fusion bonding. The fusionbonds are preferably formed simultaneously, although they can be formedseially.

FIG. 14 illustrates a proximal end region of an alternative stent 114 inwhich strands 116 a and 116 b are welded to form a strand coupling 118a, and strands 116 and 116 d are welded into a strand coupling 118 b.None of strands 116 a-d extends axially beyond the others. Thus, none ofstrands 116 is shaped to provide end closure. Instead, loop closure isprovided by a generally U-shaped strand segment 120. The U-shaped strandsegment 120 can also be referred to as a loop member. The strand segmentincludes counterparts to the elements described in connection with loopsegment 34 a, including opposed legs 122 and 124, side sections 126 and128, an apex 130, and arcuate sections 132 and 134. As can be seen inFIG. 14, a medial portion of the U-shaped strand segment 120 extendsbetween the legs 122, 124 and is formed by the side sections 126, 128and the apex 130. Also, as can be seen in FIG. 14, the ends of theU-shaped strand segment 120 and the ends of the strands 116 are orientedin opposite directions with the ends of the U-shaped strand segment 120being oriented towards a first end of the stent and the ends of thestrands 116 being oriented towards a second end of the stent. As furthershown in FIG. 14, the medial portion of the U-shaped strand segment 120is oriented so that apex 130 is oriented the same direction as the endsof the strands 116.

Strand segment 120 is attached to strand couplings 118 a and 118 b, byany of the previously mentioned connecting methods. This approachrequires connections at both strand couplings. However, it facilitatesusing different materials for strands 116 and for strand segments 120 ifdesired, and also allows attachment of the strand segments to apreviously formed stent.

FIG. 15 illustrates an alternative embodiment open-frame prosthesis 136,in which elongate strands 138 are wound about a mandrel to formmultiple, generally hexagonal cells 140. As indicated in theenlargement, adjacent cells are joined by coextensive regions 142 alongwhich strands 138 are twisted helically about one another. At a distalend 144 of the prosthesis, the strands are bent to provide loops 146. Aplurality of radiopaque markers 148 are fixed to the loops.

At a proximal end 150 of the prosthesis, pairs of strands 138 are weldedtogether to form strand couplings. Each pair of adjacent couplingsincludes one strand with an extended portion shaped into a loop segment152, which in turn is welded to the adjacent strand coupling of thepair. Radiopaque markers 153 are fixed near loop segments 152, and maybe fixed to the loop segments. Strands 138 form multiple intersections154 in addition to coextensive regions 142. Loop segments 152 can bearcuate as shown, or be shaped to more closely resemble loop segments34-44.

FIG. 16 shows a braided prosthesis 156 formed of two sets of oppositelydirected helically wound strands 158. At both ends of prosthesis 156,pairs of the strands are welded or otherwise secured together to formproximal end strand couplings 160, and distal end strand couplings 162.The prosthesis includes a plurality of proximal end loop segments 164.Each loop segment 164 is connected to an associated pair of the strandcouplings 160. Prosthesis 156 includes a plurality of distal end loopsegments 166, each coupled to an associated pair of the distal endstrand couplings.

A salient feature of the present invention is that prostheses equippedwith loop segments as previously described can be moved axially ineither direction after they are deployed, with virtually no risk oftrauma to surrounding tissue. FIG. 17 illustrates a proximal end regionof prosthesis 156, and a positioning device 168 spaced apart proximallyfrom the prosthesis. Device 168 includes an elongate flexible shaft 170,a distal portion of which is shown. A tine 172 at the distal end ofshaft 170 extends away from the shaft, inclined proximally and radiallyoutward. When shaft 170 is moved distally to position its distal end inproximate axial alignment with loop segments 164, the shaft ismanipulated to direct tine 172 through one of the loops. Then the shaftis moved proximally to carry tine 172 into engagement with an associatedloop segment 164, whereupon further proximal travel of the shaft pullsprosthesis 156 in the proximal direction.

Initially, only the proximal region of prosthesis 156 may be pulledproximally, which causes localized axial elongation. The axialelongation radially contracts prosthesis 156 along its proximal endregion near the loop segments. This facilitates proximal movement of theprosthesis by pulling the prosthesis radially inward at least slightlyaway from the surrounding tissue. As device 168 is moved further in theproximal direction, the frictional hold is overcome and the entireprosthesis moves proximally, although a distal portion of the prosthesismay remain engaged with surrounding tissue. This is beneficial, in thatthe frictional “drag” allows a more incremental, accurate adjustment ofprosthesis position.

For a symmetrical application of the pulling force, device 168 can bereplaced with a device with several tines or shafts, to simultaneouslypull several, or all, of the loop segments.

According to another alternative, a tether can be threaded through loopsegments 164, such that proximally pulling the tether brings the loopsegments radially inward and closer together in cinch fashion.

If desired, device 168 or the aforementioned tether can be used not onlyfor incremental proximal adjustments, but for retrieval of prosthesis156. To effect distal adjustments in the prosthesis position, a devicesimilar to device 168, with a tine preferably inclined radiallyoutwardly in the distal direction, could be used to engage one of distalend loop segments 166.

While the present invention has been disclosed primarily in connectionwith self-expanding stents and other open frame prostheses of tubularconstruction, it is readily apparent that a balloon-expandableprosthesis, or any other bodily insertable device with free wire ends,can be modified with loop segments as described to reduce the risk oftrauma to tissue. Also, while the preferred embodiments involve strandcouplings formed by joining pairs of strands, such couplings can beformed with three or more strands, then connected in pairs to the loopsegments.

Thus, in accordance with the present invention, loop segments areattached to associated pairs of strand end couplings to reduce the riskof trauma to tissue, and provide a prosthesis that is radiallycompressible to a smaller diameter to facilitate intraluminal delivery.The looped ends eliminate the potential for adjacent twisted strandpairs to interlock when the prosthesis is compressed to its deliverystate, ensuring a more reliable radial expansion of the prosthesis whendeployed at the treatment site. The looped ends further facilitateincremental repositioning of the prosthesis after its deployment.

The invention claimed is:
 1. A prosthesis comprising: a plurality ofwires forming a mesh, wherein terminal ends of the plurality of wiresare Joined together at a first end of the mesh to form a plurality ofstrand junctions; and spaced apart loops at the first end of the mesh,defining a spaced apart loop for each pair of adjacent strand junctions,each spaced apart loop formed from: a first strand junction of theplurality of strand junctions consisting of a terminal end of a firstwire of the plurality of wires forming the mesh and a terminal end of asecond wire of the plurality of wires forming the mesh, a second strandjunction of the plurality of strand junctions consisting of a terminalend of a third wire of the plurality of wires forming the mesh and aterminal end of a fourth wire of the plurality of wires forming themesh, wherein the terminal end of the first wire is longer than theterminal end of the second wire to provide a strand extension extendingbeyond the terminal end of the second wire and looping back to beattached to and axially aligned with the second strand junction.
 2. Theprosthesis of claim 1, the mesh comprising a second end having loops. 3.The prosthesis of claim 2, each spaced apart loop providing a smooth,rounded, blunt end.
 4. The prosthesis of claim 2, each spaced apart loopis a blunt and flexible end termination.
 5. The prosthesis of claim 2,the spaced apart loops being equally angularly spaced apart from oneanother.
 6. The prosthesis of claim 1, the plurality of wires helicallywound in a first direction over a longitudinal length of the mesh and ina second direction over the longitudinal length of the mesh.
 7. Theprosthesis of claim 1, the first and second strand junctions secured bywelds.
 8. The prosthesis of claim 1, the first and second strandjunctions secured by adhesives.
 9. The prosthesis of claim 1, the meshhaving at least one atraumatic end.
 10. A prosthesis comprising: aplurality of wires forming a mesh having a longitudinal length, whereinterminal ends of the plurality of wires are joined together at a firstend of the mesh to form a plurality of strand junctions; and spacedapart loops at the first end of the mesh, defining a spaced apart loopfor each pair of adjacent strand junctions, each spaced apart loopformed from: a first strand junction of the plurality of strandjunctions consisting of a terminal end of a first wire of the pluralityof wires forming the mesh and a terminal end of a second wire of theplurality of wires forming the mesh secured together, a second strandjunction of the plurality of strand junctions consisting of a terminalend of a third wire of the plurality of wires forming the mesh and aterminal end of a fourth wire of the plurality of wires forming the meshsecured together, wherein the terminal end of the first wire is longerthan the terminal end of the second wire to provide a strand extensionextending beyond the terminal end of the second wire and looping back tobe attached to and axially aligned with the second strand junction; andfurther wherein: each wire of the plurality of wires comprises nitinol;the plurality of wires are helically wound in a first direction over thelongitudinal length of the mesh and in a second direction over thelongitudinal length of the mesh; and the mesh has a variable diameterwherein at least one end region of the mesh has a larger diameter than amiddle portion of the mesh.
 11. The prosthesis of claim 10, furthercomprising a second end region, wherein the second end region has alarger diameter than the middle portion.
 12. The prosthesis of claim 10,wherein the second strand junction and the strand extension are weldedtogether.
 13. The prosthesis of claim 10, wherein each spaced apart loophas an apex.
 14. A prosthesis comprising: a tubular stent having a firstend and a second end; a plurality of wires forming a mesh of the tubularstent, wherein terminal ends of the plurality of wires are joinedtogether at a first end of the tubular stent to form a plurality ofstrand junctions and each of the plurality of wires forming the meshextends from the first end of the tubular stent to the second end of thetubular stent; and spaced apart loops formed with the plurality of wiresat the first end of the tubular stent, defining a spaced apart loop foreach pair of adjacent strand junctions, each spaced apart loop formedfrom: a first strand junction of the plurality of strand junctionsconsisting of a terminal end of a first wire of the plurality of wiresforming the mesh and a terminal end of a second wire of the plurality ofwires forming the mesh, a second strand junction of the plurality ofstrand junctions consisting of a terminal end of a third wire of theplurality of wires forming the mesh and a terminal end of a fourth wireof the plurality of wires forming the mesh, wherein the terminal end ofthe first wire is longer than the terminal end of the second wire toprovide a strand extension extending beyond the terminal end of thesecond wire and looping back to be attached to and axially aligned withthe second strand junction.
 15. The prosthesis of claim 14, wherein thesecond strand junction and the strand extension are welded together. 16.The prosthesis of claim 14, the mesh having a variable diameter whereinat least one end region of the mesh has a larger diameter than a middleportion of the mesh.